If you can't find any locally, and don't mind blowing a little money for real LR, SaltwaterFish.com has a $70 special for 12# of rubble. Sounds expensive, but at least the shipping is free, so that takes a big chunk out. I talked to Elite earlier this week since I need about 10# for my sump, and they sell their rubble for $6/lb. But if you only need 10# or less, you could go that route.
Neptune's has rubble for $8/lb. Expensive, but it's that nice "RealReef" stuff. From PacificEast Aquaculture, I believe...